Novel dual cores for golf balls

ABSTRACT

The present invention is directed to a golf ball comprising a dual core component. The dual core comprises an interior center component formed from a thermoset material, a thermoplastic material, or combinations thereof. The dual core also comprises a core layer disposed about the center component, formed from a thermoset material, a thermoplastic material, or combinations thereof. The present invention golf ball may further comprise an outer core layer that surrounds the dual core. The resulting multi-layered golf ball of the present invention provides for enhanced distance without sacrificing playability or durability when compared to known golf balls.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority on U.S. patent application Ser.No. 09/048,701 filed Mar. 26, 1998, which claims priority from U.S.provisional patent application Ser. No. 60/042,439 filed Mar. 28, 1997.

FIELD OF THE INVENTION

[0002] The present invention relates to golf balls and, moreparticularly, to improved golf balls comprising a unique dual coreconfiguration. The improved golf balls provide for enhanced distance anddurability properties.

BACKGROUND OF THE INVENTION

[0003] A number of two-piece (a solid resilient center or core with amolded cover) and three-piece (a liquid or solid center, elastomericwinding about the center, and a molded cover) golf balls have beenproduced. The different types of materials utilized to formulate thecores, covers, etc. of these balls dramatically alters the balls'overall characteristics. In addition, multi-layered covers containingone or more ionomer resins have also been formulated in an attempt toproduce a golf ball having the overall distance, playability anddurability characteristics desired.

[0004] Despite the great number of materials and combinations ofmaterials utilized in prior art golf balls, there still remains a needfor an improved golf ball exhibiting superior properties.

[0005] These and other objects and features of the invention will beapparent from the following summary and description of the invention,the drawings and from the claims.

SUMMARY OF THE INVENTION

[0006] In one aspect, the present invention provides a golf ballcomprising a dual core comprising a center component and a core layerdisposed about the center component. The center component comprises athermoplastic material and the core layer comprises a thermosetmaterial.

[0007] In yet another aspect, the present invention provides amulti-layer golf ball comprising a dual core component that includes acenter component and a core layer disposed about the center component.The center component comprises a thermoset material and the core layercomprises a thermoplastic material.

[0008] In yet another embodiment, the present invention provides amulti-layer golf ball comprising a dual core, having a center componentand a core layer, both of which comprise a thermoplastic material

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a cross-sectional view of a preferred embodiment golfball in accordance with the present invention illustrating a core and acover comprising an inner layer and an outer dimpled layer;

[0010]FIG. 2 is a diametrical cross-sectional view of the preferredembodiment golf ball depicted in FIG. 1 having a core and a covercomprising an inner layer surrounding the core and an outer layer havinga plurality of dimples;

[0011]FIG. 3 is a cross-sectional view of another preferred embodimentgolf ball in accordance with the present invention comprising a dualcore component;

[0012]FIG. 4 is a cross-sectional view of yet another preferredembodiment golf ball in accordance with the present invention comprisinga dual core component;

[0013]FIG. 5 is a cross-sectional view of another preferred embodimentgolf ball in accordance with the present invention comprising a dualcore component and an outer core layer;

[0014]FIG. 6 is a cross-sectional view of yet another preferredembodiment golf ball in accordance with the present invention comprisinga dual core component and an outer core layer; and

[0015]FIG. 7 is a schematic view of an assembly used for molding apreferred embodiment golf ball in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention is directed to a golf ball comprising adual-core component. The present invention golf balls preferably utilizea multi-layer cover. However, the golf balls may instead utilizeconventional cover materials such as balata or blends of balata withelastomeric or plastic materials. The multi-layer golf ball coversinclude a first or inner layer or ply of a high acid (greater than 16weight percent acid) ionomer blend or, more preferably, a low acid (16weight percent acid or less) ionomer blend and second or outer layer orply comprised of a comparatively softer, low modulus ionomer, ionomerblend or other non-ionomeric thermoplastic or thermosetting elastomersuch as polyurethane or polyester elastomer The multi-layer golf ballsof the present invention can be of standard or enlarged size.Preferably, the inner layer or ply includes a blend of low acid ionomersand has a Shore D hardness of 70 or greater and the outer cover layercomprised of polyurethane and has a Shore D hardness of about 45 (i.e.,Shore C hardness of about 65).

[0017] The present invention golf balls utilize a unique dual-coreconfiguration. Preferably, the cores comprise (i) an interior sphericalcenter component formed from a thermoset material, a thermoplasticmaterial, or combinations thereof; and (ii) a core layer disposed aboutthe spherical center component, the core layer formed from a thermosetmaterial, a thermoplastic material, or combinations thereof. The coresmay further comprise (iii) an optional outer core layer disposed aboutthe core layer. The outer core layer may be formed from a thermosetmaterial, a thermoplastic material, or combinations thereof.

[0018] Although the present invention is primarily directed to golfballs comprising a dual core component and preferably in conjunctionwith a multi-layer cover as described herein, the present invention alsoincludes golf balls having a dual core component and conventional coverscomprising balata, various thermoplastic materials, cast polyurethanes,or any other known cover material.

[0019] It has been found that multi-layer golf balls having inner andouter cover layers exhibit higher C.O.R. values and have greater traveldistance in comparison with balls made from a single cover layer. Inaddition, it has been found that use of an inner cover layer constructedof a blend of low acid (i.e., 16 weight percent acid or less) ionomerresins produces softer compression and higher spin rates than innercover layers constructed of high acid ionomer resins. This is compoundedby the fact that the softer polyurethane outer layer adds to thedesirable “feel” and high spin rate while maintaining respectableresilience. The soft outer layer allows the cover to deform more duringimpact and increases the area of contact between the club face and thecover, thereby imparting more spin on the ball. As a result, the softpolyurethane cover provides the ball with a balata-like feel andplayability characteristics with improved distance and durability.

[0020] Consequently, the overall combination of the unique dual coreconfiguration, described in greater detail herein, and the multi-layercover construction of inner and outer cover layers made, for example,from blends of low acid ionomer resins and polyurethane results in astandard size or oversized golf ball having enhanced resilience(improved travel distance) and durability (i.e. cut resistance, etc.)characteristics while maintaining and in many instances, improving theball's playability properties.

[0021] The combination of a low acid ionomer blend inner cover layerwith a soft, relatively low modulus ionomer, polyurethane basedelastomer outer cover layer provides for good overall coefficient ofrestitution (i.e., enhanced resilience) while at the same timedemonstrating improved compression and spin. The outer cover layergenerally contributes to a more desirable feel and spin, particularly atlower swing speeds with highly lofted clubs such as half wedge shots.

[0022] Accordingly, the present invention is directed to a golf ballcomprising a dual-core configuration and an improved multi-layer coverwhich produces, upon molding each layer around a core to formulate amulti-layer cover, a golf ball exhibiting enhanced distance (i.e.,resilience) without adversely affecting, and in many instances,improving the ball's playability (hardness/softness) and/or durability(i.e., cut resistance, fatigue resistance, etc.) characteristics.

[0023]FIGS. 1 and 2 illustrate a preferred embodiment golf ball 5 inaccordance with the present invention. It will be understood that noneof the referenced figures are to scale. And so, the thicknesses andproportions of the various layers and the diameter of the various corecomponents are not necessarily as depicted. The golf ball 5 comprises amulti-layered cover 12 disposed about a core 10. The core 10 of the golfball can be formed of a solid, a liquid, or any other substances thatmay be utilized to form the novel dual core described herein. The core10 is preferably a dual core as described herein. The multi-layeredcover 12 comprises two layers: a first or inner layer or ply 14 and asecond or outer layer or ply 16. The inner layer 14 can be ionomer,ionomer blends, non-ionomer, non-ionomer blends, or blends of ionomerand non-ionomer. The outer layer 16 is softer than the inner layer andcan be ionomer, ionomer blends, non-ionomer, non-ionomer blends orblends of ionomer and non-ionomer.

[0024] In a first preferred embodiment, the inner layer 14 is comprisedof a high acid (i.e., greater than 16 weight percent acid) ionomer resinor high acid ionomer blend. Preferably, the inner layer is comprised ofa blend of two or more high acid (i.e., at least 16 weight percent acid)ionomer resins neutralized to various extents by different metalcations. The inner cover layer may or may not include a metal stearate(e.g., zinc stearate) or other metal fatty acid salt. The purpose of themetal stearate or other metal fatty acid salt is to lower the cost ofproduction without affecting the overall performance of the finishedgolf ball. In a second embodiment, the inner layer 14 is comprised of alow acid (i.e., 16 weight percent acid or less) ionomer blend.Preferably, the inner layer is comprised of a blend of two or more lowacid (i.e., 16 weight percent acid or less) ionomer resins neutralizedto various extents by different metal cations. The inner cover layer mayor may not include a metal stearate (e.g., zinc stearate) or other metalfatty acid salt. The purpose of the metal stearate or other metal fattyacid salt is to lower the cost of production without affecting theoverall performance of the finished golf ball.

[0025] Two principal properties involved in golf ball performance areresilience and hardness. Resilience is determined by the coefficient ofrestitution (C.O.R.), the constant “e” which is the ratio of therelative velocity of an elastic sphere after direct impact to thatbefore impact. As a result, the coefficient of restitution (“e”) canvary from 0 to 1, with 1 being equivalent to a perfectly or completelyelastic collision and 0 being equivalent to a perfectly or completelyinelastic collision.

[0026] Resilience (C.O.R.), along with additional factors such as clubhead speed, angle of trajectory and ball configuration (i.e., dimplepattern) generally determine the distance a ball will travel when hit.Since club head speed and the angle of trajectory are factors not easilycontrollable by a manufacturer, factors of concern among manufacturersare the coefficient of restitution (C.O.R.) and the surfaceconfiguration of the ball.

[0027] The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a dual core (i.e., balls comprising an interiorspherical center component, a core layer disposed about the sphericalcenter component, and a cover), the coefficient of restitution is afunction of not only the composition of the cover, but also thecomposition and physical characteristics of the interior sphericalcenter component and the core layer. Both the dual core and the covercontribute to the coefficient of restitution in the golf balls of thepresent invention.

[0028] In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to the incoming velocity. Thecoefficient of restitution must be carefully controlled in allcommercial golf balls in order for the ball to be within thespecifications regulated by the United States Golf Association(U.S.G.A.). Along this line, the U.S.G.A. standards indicate that a“regulation” ball cannot have an initial velocity (i.e., the speed ofthe club) exceeding 255 feet per second. Since the coefficient ofrestitution of a ball is related to the ball's initial velocity, it ishighly desirable to produce a ball having sufficiently high coefficientof restitution to closely approach the U.S.G.A. limit on initialvelocity, while having an ample degree of softness (i.e., hardness) toproduce enhanced playability (i.e., spin, etc.).

[0029] The hardness of the ball is the second principal propertyinvolved in the performance of a golf ball. The hardness of the ball canaffect the playability of the ball on striking and the sound or “click”produced. Hardness is determined by the deformation (i.e., compression)of the ball under various load conditions applied across the ball'sdiameter (i.e., the lower the compression value, the harder thematerial). As indicated in U.S. Pat. No. 4,674,751, softer covers permitthe accomplished golfer to impart increased spin. This is because thesofter covers deform on impact significantly more than balls having“harder” ionomeric resin covers. As a result, the better player isallowed to impart fade, draw or backspin to the ball thereby enhancingplayability. Such properties may be determined by various spin ratetests.

[0030] It has been found that a hard inner cover layer provides for asubstantial increase in resilience (i.e., enhanced distance) over knownmulti-layer covered balls. The softer outer cover layer provides fordesirable “feel” and high spin rate while maintaining respectableresiliency. The soft outer layer allows the cover to deform more duringimpact and increases the area of contact between the club face and thecover, thereby imparting more spin on the ball. As a result, the softcover provides the ball with a balata-like feel and playabilitycharacteristics with improved distance and durability. Consequently, theoverall combination of the inner and outer cover layers and the uniquedual core configuration results in a golf ball having enhancedresilience (improved travel distance) and durability (i.e., cutresistance, etc.) characteristics while maintaining and in manyinstances, improving the playability properties of the ball.

[0031] The combination of a dual core component and a hard inner coverlayer with a soft, relatively low modulus ionomer, ionomer blend orother non-ionomeric thermoplastic elastomer outer cover layer providesfor excellent overall coefficient of restitution (i.e., excellentresilience) because of the improved resiliency produced by the innercover layer. Moreover, the configuration of, and the ability to selectthe materials used in, the dual core component enables the formulator toreadily tailor the end properties and characteristics of the resultinggolf ball. While some improvement in resiliency is also produced by theouter cover layer, the outer cover layer generally provides for a moredesirable feel and high spin, particularly at lower swing speeds withhighly lofted clubs such as half wedge shots. Inner Cover Layer Theinner cover layer is harder than the outer cover layer and generally hasa thickness in the range of 0.01 to 0.10 inches, preferably 0.03 to 0.07inches for a 1.68 inch ball and 0.05 to 0.10 inches for a 1.72 inch (ormore) ball. The core and inner cover layer together form an inner ballhaving a coefficient of restitution of 0.780 or more and more preferably0.790 or more, and a diameter in the range of 1.48-1.66 inches for a1.68 inch ball and 1.50-1.70 inches for a 1.72 inch (or more) ball. Theinner cover layer has a Shore D hardness of 60 or more. It isparticularly advantageous if the golf balls of the invention have aninner layer with a Shore D hardness of 65 or more. The above-describedcharacteristics of the inner cover layer provide an inner ball having aPGA compression of 100 or less. It is found that when the inner ball hasa PGA compression of 90 or less, excellent playability results.

[0032] The inner layer compositions include the high acid ionomers suchas those developed by E.I. DuPont de Nemours & Company under thetrademark “Surlyn(D” and by Exxon Corporation under the trademark“Escor®” or trade name “Iotek”, or blends thereof. Examples ofcompositions which may be used as the inner layer herein are set forthin detail in a continuation of U.S. application Ser. No. 08/174,765,which is a continuation of U.S. application Ser. No. 07/776,803 filedOct. 15, 1991, and Ser. No. 08/493,089, which is a continuation of Ser.No. 07/981,751, which in turn is a continuation of Ser. No. 07/901,660filed Jun. 19, 1992, all of which are incorporated herein by reference.Of course, the inner layer high acid ionomer compositions are notlimited in any way to those compositions set forth in said applications.

[0033] The high acid ionomers which may be suitable for use informulating the inner layer compositions are ionic copolymers which arethe metal, i.e., sodium, zinc, magnesium, etc., salts of the reactionproduct of an olefin having from about 2 to 8 carbon atoms and anunsaturated monocarboxylic acid having from about 3 to 8 carbon atoms.Preferably, the ionomeric resins are copolymers of ethylene and eitheracrylic or methacrylic acid. In some circumstances, an additionalcomonomer such as an acrylate ester (i.e., iso- or n-butylacrylate,etc.) can also be included to produce a softer terpolymer. Thecarboxylic acid groups of the copolymer are partially neutralized (i.e.,approximately 10-100%, preferably 30-70%) by the metal ions. Each of thehigh acid ionomer resins which may be included in the inner layer covercompositions of the invention contains greater than about 16% by weightof a carboxylic acid, preferably from about 17% to about 25% by weightof a carboxylic acid, more preferably from about 18.5% to about 21.5% byweight of a carboxylic acid.

[0034] Although the inner layer cover composition of several embodimentsof the present invention preferably includes a high acid ionomericresin, the scope of the patent embraces all known high acid ionomericresins falling within the parameters set forth above. Only a relativelylimited number of these high acid ionomeric resins have recently becomecommercially available.

[0035] The high acid ionomeric resins available from Exxon under thedesignation “Escor®” and or “Iotek”, are somewhat similar to the highacid ionomeric resins available under the “SurlynO” trademark. However,since the Escor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

[0036] Examples of the high acid methacrylic acid based ionomers foundsuitable for use in accordance with this invention include Surlyn®8220and 8240 (both formerly known as forms of Surlyn AD-8422), Surlyn®9220(zinc cation), Surlyn®SEP-503-1 (zinc cation), and Surlyn®SEP-503-2(magnesium cation). According to DuPont, all of these ionomers containfrom about 18.5 to about 21.5% by weight methacrylic acid.

[0037] More particularly, Surlyn® AD-8422 is currently commerciallyavailable from DuPont in a number of different grades (i.e., AD-8422-2,AD-8422-3, AD-8422-5, etc.) based upon differences in melt index.According to DuPont, Surlyn® 8422, which is believed recently to havebeen redesignated as 8220 and 8240, offers the following generalproperties when compared to Surlyn® 8920, the stiffest, hardest of allon the low acid grades (referred to as “hard” ionomers in U.S. Pat. No.4,884,814): LOW ACID (15 wt % HIGH ACID Acid) (>20 wt % Acid) SURLYN ®SURLYN ® SURLYN ® 8920 8422-2 8422-3 IONOMER Cation Na Na Na Melt Index1.2 2.8 1.0 Sodium, Wt % 2.3 1.9 2.4 Base Resin MI 60 60 60 MP¹, ° C. 8886 85 FP¹, ° C. 47 48.5 45 COMPRESSION MOLDING² Tensile Break, 4350 41905330 psi Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod,53.2 76.4 88.3 K psi Shore D 66 67 68 hardness

[0038] In comparing Surlyn® 8920 to Surlyn® 8422-2 and Surlyn® 8422-3,it is noted that the high acid Surlyn® 8422-2 and 8422-3 ionomers have ahigher tensile yield, lower elongation, slightly higher Shore D hardnessand much higher flexural modulus. Surlyn® 8920 contains 15 weightpercent methacrylic acid and is 59% neutralized with sodium.

[0039] In addition, Surlyn®SEP-503-1 (zinc cation) and Surlyn®SEP-503-2(magnesium cation) are high acid zinc and magnesium versions of theSurlyn®AD 8422 high acid ionomers. When compared to the Surlyn® AD 8422high acid ionomers, the Surlyn® SEP-503-1 and SEP-503-2 ionomers can bedefined as follows: Surlyn ® Ionomer Ion Melt Index Neutralization % AD8422-3 Na 1.0 45 SEP 503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43

[0040] Further, Surlyn® 8162 is a zinc cation ionomer resin containingapproximately 20% by weight (i.e., 18.5 -21.5% weight) methacrylic acidcopolymer that has been 30-70% neutralized. Surlyn® 8162 is currentlycommercially available from DuPont.

[0041] Examples of the high acid acrylic acid based ionomers suitablefor use in the present invention also include the Escor® or Iotek highacid ethylene acrylic acid ionomers produced by Exxon such as Ex 1001,1002, 959, 960, 989, 990, 1003, 1004, 993, 994. In this regard, Escor®or Iotek 959 is a sodium ion neutralized ethylene-acrylic neutralizedethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960contain from about 19.0 to 21.0% by weight acrylic acid withapproximately 30 to about 70 percent of the acid groups neutralized withsodium and zinc ions, respectively. The physical properties of thesehigh acid acrylic acid based ionomers are set forth in Tables 1 and 2 asfollows: TABLE 1 Physical Properties of Various Ionomers ESCOR ® ESCOR ®PRO- (IOTEK) (IOTEK) PERTY Ex1001 Ex1002 959 Ex1003 Ex1004 960 Melt 1.01.6 2.0 1.1 2.0 1.8 index, g/10 min Cation Na Na Na Zn Zn Zn Melting 183183 172 180 180.5 174 Point, ° F. Vicat 125 125 130 133 131 131Softening Point, ° F. Tensile 34.4 22.5 4600 24.8 20.6 3500 @ Break MPaMPa psi MPa MPa psi Elongation 341 348 325 387 437 430 @ Break, %Hardness, 63 62 66 54 53 57 Shore D Flexural 365 380 66,000 147 13027,000 Modulus MPa MPa psi MPa MPa psi

[0042] TABLE 2 Physical Properties of Various Ionomers PROPERTY UNITS EX989 EX 993 EX 994 EX 990 Melt index g/10 min 1.30 1.25 1.32 1.24Moisture ppm 482 214 997 654 Cation type — Na Li K Zn M+ content by AASwt % 2.74 0.87 4.54 0 Zn content by AAS wt % 0 0 0 3.16 Density kg/m³959 945 976 977 Vicat softening point ° C. 52.5 51 50 55.0Crystallization point ° C. 40.1 39.8 44.9 54.4 Melting point ° C. 82.681.0 80.4 81.0 Tensile at yield MPa 23.8 24.6 22 16.5 Tensile at breakMPa 32.3 31.1 29.7 23.8 Elongation at break % 330 260 340 357 1% secantmodulus MPa 389 379 312 205 Flexural modulus MPa 340 368 303 183Abrasion resistance mg 20.0 9.2 15.2 20.5 Hardness Shore D — 62 62.5 6156 Zwick Rebound % 61 63 59 48

[0043] Furthermore, as a result of the development by the assignee ofthis application of a number of new high acid ionomers neutralized tovarious extents by several different types of metal cations, such as bymanganese, lithium, potassium, calcium and nickel cations, several newhigh acid ionomers and/or high acid ionomer blends besides sodium, zincand magnesium high acid ionomers or ionomer blends are now available forgolf ball cover production. It has been found that these new cationneutralized high acid ionomer blends produce inner cover layercompositions exhibiting enhanced hardness and resilience due tosynergies which occur during processing. Consequently, the metal cationneutralized high acid ionomer resins recently produced can be blended toproduce substantially higher C.O.R.'s than those produced by the lowacid ionomer inner cover compositions presently commercially available.

[0044] More particularly, several new metal cation neutralized high acidionomer resins have been produced by the inventors by neutralizing, tovarious extents, high acid copolymers of an alpha-olefin and an alpha,beta-unsaturated carboxylic acid with a wide variety of different metalcation salts. This discovery is the subject matter of U.S. applicationSer. No. 08/493,089, incorporated herein by reference. It has been foundthat numerous new metal cation neutralized high acid ionomer resins canbe obtained by reacting a high acid copolymer (i.e., a copolymercontaining greater than 16% by weight acid, preferably from about 17 toabout 25 weight percent acid, and more preferably about 20 weightpercent acid), with a metal cation salt capable of ionizing orneutralizing the copolymer to the extent desired (i.e., from about 10%to 90%).

[0045] The base copolymer is made up of greater than 16% by weight of analpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally,a softening comonomer can be included in the copolymer. Generally, thealpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene,and the unsaturated carboxylic acid is a carboxylic acid having fromabout 3 to 8 carbons. Examples of such acids include acrylic acid,methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid,maleic acid, fumaric acid, and itaconic acid, with acrylic acid beingpreferred.

[0046] The softening comonomer that can be optionally included in theinner cover layer for the golf ball of the invention may be selectedfrom the group consisting of vinyl esters of aliphatic carboxylic acidswherein the acids have 2 to 10 carbon atoms, vinyl ethers wherein thealkyl groups contains 1 to 10 carbon atoms, and alkyl acrylates ormethacrylates wherein the alkyl group contains 1 to 10 carbon atoms.Suitable softening comonomers include vinyl acetate, methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate,butyl methacrylate, or the like.

[0047] Consequently, examples of a number of copolymers suitable for useto produce the high acid ionomers included in the present inventioninclude, but are not limited to, high acid embodiments of anethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer,an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer,an ethylene/methacrylic acid/vinyl acetate copolymer, anethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymerbroadly contains greater than 16% by weight unsaturated carboxylic acid,from about 39 to about 83% by weight ethylene and from 0 to about 40% byweight of a softening comonomer. Preferably, the copolymer containsabout 20% by weight unsaturated carboxylic acid and about 80% by weightethylene. Most preferably, the copolymer contains about 20% acrylic acidwith the remainder being ethylene.

[0048] Along these lines, examples of the preferred high acid basecopolymers which fulfill the criteria set forth above, are a series ofethylene-acrylic copolymers which are commercially available from TheDow Chemical Company, Midland, Michigan, under the “Primacor”designation. These high acid base copolymers exhibit the typicalproperties set forth below in Table 3. TABLE 3 Typical Properties ofPrimacor Ethylene-Acrylic Acid Copolymers MELT TENSILE FLEXURAL VICATPERCENT DENSITY, INDEX, YD. ST MODULUS SOFT PT SHORE D GRADE ACID glccg/10 min (psi) (psi) (° C.) HARDNESS ASTM D-792 D-1238 D-638 D-790D-1525 D-2240 5980 20.0 0.958  300.0 — 4800 43 50 5990 20.0 0.955 1300.0650 2600 40 42 5990 20.0 0.955 1300.0 650 3200 40 42 5981 20.0 0.960 300.0 900 3200 46 48 5981 20.0 0.960  300.0 900 3200 46 48 5983 20.00.958  500.0 850 3100 44 45 5991 20.0 0.953 2600.0 635 2600 38 40

[0049] Due to the high molecular weight of the Primacor 5981 grade ofthe ethylene-acrylic acid copolymer, this copolymer is the morepreferred grade utilized in the invention.

[0050] The metal cation salts utilized in the invention are those saltswhich provide the metal cations capable of neutralizing, to variousextents, the carboxylic acid groups of the high acid copolymer. Theseinclude acetate, oxide or hydroxide salts of lithium, calcium, zinc,sodium, potassium, nickel, megnesium, and manganese.

[0051] Examples of such lithium ion sources are lithium hydroxidemonohydrate, lithium hydroxide, lithium oxide and lithium acetate.Sources for the calcium ion include calcium hydroxide, calcium acetateand calcium oxide. Suitable zinc ion sources are zinc acetate dihydrateand zinc acetate, a blend of zinc oxide and acetic acid. Examples ofsodium ion sources are sodium hydroxide and sodium acetate. Sources forthe potassium ion include potassium hydroxide and potassium acetate.Suitable nickel ion sources are nickel acetate, nickel oxide and nickelhydroxide. Sources of magnesium include magnesium oxide, magnesiumhydroxide, magnesium acetate. Sources of manganese include manganeseacetate and manganese oxide.

[0052] The new metal cation neutralized high acid ionomer resins areproduced by reacting the high acid base copolymer with various amountsof the metal cation salts above the crystalline melting point of thecopolymer, such as at a temperature from about 200° F. to about 500° F.,preferably from about 250° F. to about 350° F. under high shearconditions at a pressure of from about 10 psi to 10,000 psi. Other wellknown blending techniques may also be used. The amount of metal cationsalt utilized to produce the new metal cation neutralized high acidbased ionomer resins is the quantity which provides a sufficient amountof the metal cations to neutralize the desired percentage of thecarboxylic acid groups in the high acid copolymer. The extent ofneutralization is generally from about 10% to about 90%.

[0053] As indicated below in Table 4 and more specifically in Example 1in U.S. application Ser. No. 08/493,089, a number of new types of metalcation neutralized high acid ionomers can be obtained from the aboveindicated process. These include new high acid ionomer resinsneutralized to various extents with manganese, lithium, potassium,calcium and nickel cations. In addition, when a high acidethylene/acrylic acid copolymer is utilized as the base copolymercomponent of the invention and this component is subsequentlyneutralized to various extents with the metal cation salts producingacrylic acid based high acid ionomer resins neutralized with cationssuch as sodium, potassium, lithium, zinc, magnesium, manganese, calciumand nickel, several new cation neutralized acrylic acid based high acidionomer resins are produced. TABLE 4 Metal Cation Neutralized High AcidIonomers Shore D Formulation Wt-% Wt-% Melt Hard No. Cation SaltNeutralization Index C.O.R. ness 1(NaOH) 6.98 67.5 0.9 .804 71 2(NaOH)5.66 54.0 2.4 .808 73 3(NaOH) 3.84 35.9 12.2 .812 69 4(NaOH) 2.91 27.017.5 .812 (brittle) 5(MnAc) 19.6 71.7 7.5 .809 73 6(MnAc) 23.1 88.3 3.5.814 77 7(MnAc) 15.3 53.0 7.5 .810 72 8(MnAc) 26.5 106 0.7 .813(brittle) 9(LiOH) 4.54 71.3 0.6 .810 74 10(LiOH) 3.38 52.5 4.2 .818 7211(LiOH) 2.34 35.9 18.6 .815 72 12(KOH) 5.30 36.0 19.3 Broke 70 13(KOH)8.26 57.9 7.18 .804 70 14(KOH) 10.7 77.0 4.3 .801 67 15(ZnAc) 17.9 71.50.2 .806 71 16(ZnAc) 13.9 53.0 0.9 .797 69 l7(ZnAc) 9.91 36.1 3.4 .79367 18(MgAc) 17.4 70.7 2.8 .814 74 19(MgAc) 20.6 87.1 1.5 .815 7620(MgAc) 13.8 53.8 4.1 .814 74 21(CaAc) 13.2 69.2 1.1 .813 74 22(CaAc)7.12 34.9 10.1 .808 70 23(MgO) 2.91 53.5 2.5 .813 24(MgO) 3.85 71.5 2.8.808 25(MgO) 4.76 89.3 1.1 .809 26(MgO) 1.96 35.7 7.5 .815 27(NiAc)13.04 61.1 0.2 .802 71 28(NiAc) 10.71 48.9 0.5 .799 72 29(NiAc) 8.2636.7 1.8 .796 69 30(NiAc) 5.66 24.4 7.5 .786 64

[0054] When compared to low acid versions of similar cation neutralizedionomer resins, the new metal cation neutralized high acid ionomerresins exhibit enhanced hardness, modulus and resiliencecharacteristics. These are properties that are particularly desirable ina number of thermoplastic fields, including the field of golf ballmanufacturing.

[0055] When utilized in the construction of the inner layer of amulti-layered golf ball, it has been found that the new acrylic acidbased high acid ionomers extend the range of hardness beyond thatpreviously obtainable while maintaining the beneficial properties (i.e.durability, click, feel, etc.) of the softer low acid ionomer coveredballs, such as balls produced utilizing the low acid ionomers disclosedin U.S. Pat. Nos. 4,884,814 and 4,911,451.

[0056] Moreover, as a result of the development of a number of newacrylic acid based high acid ionomer resins neutralized to variousextents by several different types of metal cations, such as manganese,lithium, potassium, calcium and nickel cations, several new ionomers orionomer blends are now available for production of an inner cover layerof a multi-layered golf ball. By using these high acid ionomer resins,harder, stiffer inner cover layers having higher C.O.R.s, and thuslonger distance, can be obtained.

[0057] More preferably, it has been found that when two or more of theabove-indicated high acid ionomers, particularly blends of sodium andzinc high acid ionomers, are processed to produce the covers of multi-layered golf balls, (i.e., the inner cover layer herein) the resultinggolf balls will travel further than previously known multi-layered golfballs produced with low acid ionomer resin covers due to the balls'enhanced coefficient of restitution values.

[0058] The low acid ionomers which may be suitable for use informulating the inner layer compositions of several of the embodimentsof the subject invention are ionic copolymers which are the metal, i.e.,sodium, zinc, magnesium, etc., salts of the reaction product of anolefin having from about 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from about 3 to 8 carbon atoms. Preferably,the ionomeric resins are copolymers of ethylene and either acrylic ormethacrylic acid. In some circumstances, an additional comonomer such asan acrylate ester (i.e., iso- or n-butylacrylate, etc.) can also beincluded to produce a softer terpolymer. The carboxylic acid groups ofthe copolymer are partially neutralized (i.e., approximately 10-100%,preferably 30-70%) by the metal ions. Each of the low acid ionomerresins which may be included in the inner layer cover compositions ofthe invention contains 16% by weight of less of a carboxylic acid.

[0059] The inner layer compositions include the low acid ionomers suchas those developed and sold by E.I. DuPont de Nemours & Company underthe trademark “Surlyno” and by Exxon Corporation under the trademark“Escor®” or tradename “Iotek,” or blends thereof.

[0060] The low acid ionomer resins available from Exxon under thedesignation “Escor®” and/or “Iotek,” are somewhat similar to the lowacid ionomeric resins available under the “Surlyn®” trademark. However,since the Escor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

[0061] When utilized in the construction of the inner layer of amulti-layered golf ball, it has been found that the low acid ionomerblends extend the range of compression and spin rates beyond thatpreviously obtainable. More preferably, it has been found that when twoor more low acid ionomers, particularly blends of sodium and zincionomers, are processed to produce the covers of multi-layered golfballs, (i.e., the inner cover layer herein) the resulting golf ballswill travel further and at an enhanced spin rate than previously knownmulti-layered golf balls. Such an improvement is particularly noticeablein enlarged or oversized golf balls.

[0062] The use of an inner layer formulated from blends of lower acidionomers produces multi-layer golf balls having enhanced compression andspin rates. These are the properties desired by the more skilled golfer.

[0063] In yet another embodiment of the inner cover layer, a blend ofhigh and low acid ionomer resins is used. These can be the ionomerresins described above, combined in a weight ratio which preferably iswithin the range of 10:90 to 90:10 parts of high and low acid ionomerresins.

[0064] A further additional embodiment of the inner cover layer isprimarily based upon the use of a fully non-ionomeric thermoplasticmaterial. Suitable non- ionomeric materials include metallocenecatalyzed polyolefins or polyamides, polyamide/ionomer blends,polyphenylene ether/ionomer blends, etc., which have a shore D hardnessof >60 and a flex modulus of greater than about 30,000 psi, or otherhardness and flex modulus values which are comparable to the propertiesof the ionomers described above. Other suitable materials include, butare not limited to, thermoplastic or thermosetting polyurethanes, apolyester elastomer such as that marketed by DuPont under the trademarkHytrel®, or a polyester amide such as that marketed by Elf Atochem S. A.under the trademark Pebax®, a blend of two or more non-ionomericthermoplastic elastomers, or a blend of one or more ionomers and one ormore non-ionomeric thermoplastic elastomers. These materials can beblended with the ionomers described above in order to reduce costrelative to the use of higher quantities of ionomer.

[0065] Outer Cover Layer

[0066] While the dual core component described below, and the hard innercover layer formed thereon, provide the multi-layer golf ball with powerand distance, the outer cover layer 16 is comparatively softer than theinner cover layer. The softness provides for the feel and playabilitycharacteristics typically associated with balata or balata-blend balls.The outer cover layer or ply is comprised of a relatively soft, lowmodulus (about 1,000 psi to about 10,100 psi) and, in an alternateembodiment, low acid (less than 16 weight percent acid) ionomer, anionomer blend, a non-ionomeric thermoplastic or thermosetting materialsuch as, but not limited to, a metallocene catalyzed polyolefin such asEXACT material available from EXXON, a polyurethane, a polyesterelastomer such as that marketed by DuPont under the trademark Hytrel®,or a polyester amide such as that marketed by Elf Atochem S. A. underthe trademark Pebax®, a blend of two or more non-ionomeric thermoplasticor thermosetting materials, or a blend of one or more ionomers and oneor more non-ionomeric thermoplastic materials. The outer layer is fairlythin (i.e. from about 0.010 to about 0.10 inches in thickness, moredesirably 0.03 to 0.06 inches in thickness for a 1.680 inch ball and0.04 to 0.07 inches in thickness for a 1.72 inch or more ball), butthick enough to achieve desired playability characteristics whileminimizing expense. Thickness is defined as the average thickness of thenon-dimpled areas of the outer cover layer. The outer cover layer, suchas layer 16, 16 has a Shore D hardness of 55 or less, and morepreferably 50 or less.

[0067] In one embodiment, the outer cover layer preferably is formedfrom an ionomer which constitutes at least 75 weight % of an acrylateester-containing ionic copolymer or blend of acrylate ester-containingionic copolymers. This type of outer cover layer in combination with thecore and inner cover layer described above results in golf ball covershaving a favorable combination of durability and spin rate. The one ormore acrylate ester-containing ionic copolymers each contain an olefin,an acrylate ester, and an acid. In a blend of two or more acrylateester-containing ionic copolymers, each copolymer may contain the sameor a different olefin, acrylate ester and acid than are contained in theother copolymers. Preferably, the acrylate ester-containing ioniccopolymer or copolymers are terpolymers, but additional monomers can becombined into the copolymers if the monomers do not substantially reducethe scuff resistance or other good playability properties of the cover.

[0068] For a given copolymer, the olefin is selected from the groupconsisting of olefins having 2 to 8 carbon atoms, including, asnon-limiting examples, ethylene, propylene, butene-1, hexene-1 and thelike. Preferably the olefin is ethylene.

[0069] The acrylate ester is an unsaturated monomer having from 1 to 21carbon atoms which serves as a softening comonomer. The acrylate esterpreferably is methyl, ethyl, n-propyl, n-butyl, n-octyl, 2-ethylhexyl,or 2-methoxyethyl 1-acrylate, and most preferably is methyl acrylate orn-butyl acrylate. Another suitable type of softening comonomer is analkyl vinyl ether selected from the group consisting of n-butyl,n-hexyl, 2-ethylhexyl, and 2-methoxyethyl vinyl ethers.

[0070] The acid is a mono- or dicarboxylic acid and preferably isselected from the group consisting of methacrylic, acrylic, ethacrylic,a-chloroacrylic, crotonic, maleic, fumaric, and itaconic acid, or thelike, and half esters of maleic, fumaric and itaconic acid, or the like.The acid group of the copolymer is 10-100% neutralized with any suitablecation, for example, zinc, sodium, magnesium, lithium, potassium,calcium, manganese, nickel, chromium, tin, aluminum, or the like. It hasbeen found that particularly good results are obtained when theneutralization level is about 50-100%.

[0071] The one or more acrylate ester-containing ionic copolymers eachhas an individual Shore D hardness of about 5-64. The overall Shore Dhardness of the outer cover is 55 or less, and generally is 40-55. It ispreferred that the overall Shore D hardness of the outer cover is in therange of 40-50 in order to impart particularly good playabilitycharacteristics to the ball.

[0072] The outer cover layer of the invention is formed over a core toresult in a golf ball having a coefficient of restitution of at least0.770, more preferably at least 0.780, and most preferably at least0.790. The coefficient of restitution of the ball will depend upon theproperties of both the core and the cover. The PGA compression of thegolf ball is 100 or less, and preferably is 90 or less.

[0073] The acrylate ester-containing ionic copolymer or copolymers usedin the outer cover layer can be obtained by neutralizing commerciallyavailable acrylate ester-containing acid copolymers such aspolyethylene-methyl acrylate-acrylic acid terpolymers, including ESCORATX (Exxon Chemical Company) or poly (ethylene-butylacrylate-methacrylic acid) terpolymers, including NUCREL (DuPontChemical Company). Particularly preferred commercially availablematerials include ATX 320, ATX 325, ATX 310, ATX 350, and blends ofthese materials with NUCREL 010 and NUCREL 035. The acid groups of thesematerials and blends are neutralized with one or more of various cationsalts including zinc, sodium, magnesium, lithium, potassium, calcium,manganese, nickel, etc. The degree of neutralization ranges from10-100%. Generally, a higher degree of neutralization results in aharder and tougher cover material. The properties of non-limitingexamples of commercially available un-neutralized acid terpolymers whichcan be used to form the golf ball outer cover layers of the inventionare provided below in Table 5. TABLE 5 Properties of Un-Neutralized AcidTerpolymers Flex Melt Index Modulus dg/min Acid No. MPa Hardness TradeName ASTM D 1238 % KOH/g (ASTM D790) (Shore D) ATX 310 6 45 80 44 ATX320 5 45 50 34 ATX 325 20  45  9 30 ATX 350 6 15 20 28 Nucrel 010 11  6040 40 Nucrel 035 35  60 59 40

[0074] The ionomer resins used to form the outer cover layers can beproduced by reacting the acrylate ester-containing acid copolymer withvarious amounts of the metal cation salts at a temperature above thecrystalline melting point of the copolymer, such as a temperature fromabout 200° F. to about 500° F., preferably from about 250° F. to about350° F., under high shear conditions at a pressure of from about 100 psito 10,000 psi. Other well known blending techniques may also be used.The amount of metal cation salt utilized to produce the neutralizedionic copolymers is the quantity which provides a sufficient amount ofthe metal cations to neutralize the desired percentage of the carboxylicacid groups in the high acid copolymer. When two or more differentcopolymers are to be used, the copolymers can be blended before or afterneutralization. Generally, it is preferable to blend the copolymersbefore they are neutralized to provide for optimal mixing.

[0075] The compatibility of the acrylate ester-containing copolymerswith each other in a copolymer blend produces a golf ball outer coverlayer having a surprisingly good scuff resistance for a given hardnessof the outer cover layer. The golf ball according to the invention has ascuff resistance of no higher than 3.0. It is preferred that the golfball has a scuff resistance of no higher than about 2.5 to ensure thatthe golf ball is scuff resistant when used in conjunction with a varietyof types of clubs, including sharp-grooved irons, which are particularlyinclined to result in scuffing of golf ball covers. The best resultsaccording to the invention are obtained when the outer cover layer has ascuff resistance of no more than about 2.0.

[0076] Additional materials may also be added to the inner and outercover layer of the present invention as long as they do notsubstantially reduce the playability properties of the ball. Suchmaterials include dyes (for example, Ultramarine Blue sold by Whitaker,Clark, and Daniels of South Plainsfield, N.J.) (see U.S. Pat. No.4,679,795), pigments such as titanium dioxide, zinc oxide, bariumsulfate and zinc sulfate; UV absorbers; antioxidants; antistatic agents;optical brighteners; and stabilizers. Moreover, the cover compositionsof the present invention may also contain softening agents such as thosedisclosed in U.S. Pat. Nos. 5,312,857 and 5,306,760, includingplasticizers, metal stearates, processing acids, etc., and reinforcingmaterials such as glass fibers and inorganic fillers, as long as thedesired properties produced by the golf ball covers of the invention arenot impaired.

[0077] The outer layer in another embodiment of the invention includes ablend of a soft (low acid) ionomer resin with a small amount of a hard(high acid) ionomer resin. A low modulus ionomer suitable for use in theouter layer blend has a flexural modulus measuring from about 1,000 toabout 10,000 psi, with a hardness of about 20 to about 40 on the Shore Dscale. A high modulus ionomer herein is one which measures from about15,000 to about 70,000 psi as measured in accordance with ASTM methodD-790. The hardness may be defined as at least 50 on the Shore D scaleas measured in accordance with ASTM method D-2240.

[0078] Soft ionomers primarily are used in formulating the hard/softblends of the cover compositions. These ionomers include acrylic acidand methacrylic acid based soft ionomers. They are generallycharacterized as comprising sodium, zinc, or other mono- or divalentmetal cation salts of a terpolymer of an olefin having from about 2 to 8carbon atoms, methacrylic acid, acrylic acid, or another, α, β-unsaturated carboxylic acid, and an unsaturated monomer of the acrylateester class having from 1 to 21 carbon atoms. The soft ionomer ispreferably made from an acrylic acid base polymer is an unsaturatedmonomer of the acrylate ester class.

[0079] Certain ethylene-acrylic acid based soft ionomer resins developedby the Exxon Corporation under the designation “Iotek 7520” (referred toexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) may be combined with known hardionomers such as those indicated above to produce the inner and outercover layers. The combination produces higher C.O.R.s at equal or softerhardness, higher melt flow (which corresponds to improved, moreefficient molding, i.e., fewer rejects] as well as significant costsavings versus the outer layer of multi-layer balls produced by otherknown hard-soft ionomer blends as a result of the lower overall rawmaterials cost and improved yields.

[0080] While the exact chemical composition of the resins to be sold byExxon under the designation Iotek 7520 is considered by Exxon to beconfidential and proprietary information, Exxon's experimental productdata sheet lists the following physical properties of the ethyleneacrylic acid zinc ionomer developed by Exxon: TABLE 6 PhysicalProperties of Iotek 7520 Property Value ASTM Method Units Typical MeltIndex D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962 Cation Zinc MeltingPoint D-3417 ° C. 66 Crystallization D-3417 ° C. 49 Point VicatSoftening D-1525 ° C. 42 Point Plaque properties (2 mm thick CompressionMolded Plaques) Tensile at Break D-638 MPa 10 Yield Point D-638 MPa NoneElongation at Break D-638 % 760 1% Secant Modulus D-638 MPa 22 Shore DHardness D-2240 32 Flexural Modulus D-790 MPa 26 Zwick Rebound ISO 4862% 52 De Mattia Flex D-430 Cycles >5000 Resistance

[0081] In addition, test data collected by the inventors indicates thatIotek 7520 resins have Shore D hardnesses of about 32 to 36 (per ASTMD-2240), melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTMD-1288), and a flexural modulus of about 2500-3500 psi (per ASTM D-790).Furthermore, testing by an independent testing laboratory by pyrolysismass spectrometry indicates that Iotek 7520 resins are generally zincsalts of a terpolymer of ethylene, acrylic acid, and methyl acrylate.

[0082] Furthermore, the inventors have found that a newly developedgrade of an acrylic acid based soft ionomer available from the ExxonCorporation under the designation Iotek 7510 is also effective whencombined with the hard ionomers indicated above in producing golf ballcovers exhibiting higher C.O.R. values at equal or softer hardness thanthose produced by known hard-soft ionomer blends. In this regard, Iotek7510 has the advantages (i.e. improved flow, higher C.O.R. values atequal hardness, increased clarity, etc.) produced by the Iotek 7520resin when compared to the methacrylic acid base soft ionomers known inthe art (such as the Surlyn® 8625 and Surlyn® 8629 combinationsdisclosed in U.S. Pat. No. 4,8884,814).

[0083] In addition, Iotek 7510, when compared to Iotek 7520, producesslightly higher C.O.R. values at equal softness/hardness due to theIotek 7510's higher hardness and neutralization. Similarly, Iotek 7510produces better release properties (from the mold cavities) due to itsslightly higher stiffness and lower flow rate than Iotek 7520. This isimportant in production where the soft covered balls tend to have loweryields caused by sticking in the molds and subsequent punched pin marksfrom the knockouts.

[0084] According to Exxon, Iotek 7510 is of similar chemical compositionas Iotek 7520 (i.e. a zinc salt of a terpolymer of ethylene, acrylicacid, and methyl acrylate) but is more highly neutralized. Based uponFTIR analysis, Iotek 7520 is estimated to be about 30-40 wt. %neutralized and Iotek 7510 is estimated to be about 40-60 wt. %neutralized. The typical properties of Iotek 7510 in comparison of thoseof Iotek 7520 in comparison of those of Iotek 7520 are set forth below:TABLE 7 Physical Properties of Iotek 7510 in Comparison to Iotek 7520IOTEK 7520 IOTEK 7510 MI, g/10 mm 2.0 0.8 Density, g/cc 0.96 0.97Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109 FlexModulus, psi 3800 5300 Tensile Strength, Psi 1450 1750 Elongation, % 760690 Hardness, Shore D 32 35

[0085] The hard ionomer resins utilized to produce the outer cover layercomposition hard/soft blends include ionic copolymers which are thesodium, zinc, magnesium, lithium, etc. salts of the reaction product ofan olefin having from 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from 3 to 8 carbon atoms. The carboxylic acidgroups of the copolymer may be totally or partially (i.e. approximately15-75 percent) neutralized.

[0086] The hard ionomeric resins are likely copolymers of ethylene andacrylic and/or methacrylic acid, with copolymers of ethylene and acrylicacid being the most preferred. Two or more types of hard ionomericresins may be blended into the outer cover layer compositions in orderto produce the desired properties of the resulting golf balls.

[0087] As discussed earlier herein, the hard ionomeric resins introducedunder the designation Escor® and sold under the designation “Iotek” aresomewhat similar to the hard ionomeric resins sold under the Surlyn®trademark. However, since the “Iotek” ionomeric resins are sodium orzinc salts of poly(ethylene-acrylic acid) and the Surlyn® resins arezinc or sodium salts of poly(ethylene-methacrylic acid) some distinctdifferences in properties exist. As more specifically indicated in thedata set forth below, the hard “Iotek” resins (i.e., the acrylic acidbased hard ionomer resins) are the more preferred hard resins for use informulating the outer layer blends for use in the present invention. Inaddition, various blends of “Iotek” and Surlyn® hard ionomeric resins,as well as other available ionomeric resins, may be utilized in thepresent invention in a similar manner.

[0088] Examples of commercially available hard ionomeric resins whichmay be used in the present invention in formulating the outer coverblends include the hard sodium ionic copolymer sold under the trademarkSurlyn® 8940 and the hard zinc ionic copolymer sold under the trademarkSurlyn® 9910. Surlyn® 8940 is a copolymer of ethylene with methacrylicacid and about 15 weight percent acid which is about 29 percentneutralized with sodium ions. This resin has an average melt flow indexof about 2.8. Surlyn® 9910 is a copolymer of ethylene and methacrylicacid with about 15 weight percent acid which is about 58 percentneutralized with zinc ions. The average melt flow index of Surlyn® 9910is about 0.7. The typical properties of Surlyn® 9910 and 8940 are setforth below in Table 8: TABLE 8 Typical Properties of CommerciallyAvailable Hard Surlyn ® Resins Suitable for Use in the Outer LayerBlends of the Present Invention ASTM D 8940 9910 8920 8528 9970 9730Cation Type Sodium Zinc Sodium Sodium Zinc Zinc Melt flow index, gms/10min. D-1238 2.8 0.7 0.9 1.3 14.0 1.6 Specific Gravity, D-792 0.95 0.970.95 0.94 0.95 0.95 g/cm³ Hardness, Shore D D-2240 66 64 66 60 62 63Tensile Strength, D-638 (4.8) (3.6) (5.4) (4.2) (3.2) (4.1) (kpsi), MPa33.1 24.8 37.2 29.0 22.0 28.0 Elongation, % D-638 470 290 350 450 460460 Flexural Modulus, D-790 (51) (48) (55) (32) (28) (30) (kpsi) MPa 350330 380 220 190 210 Tensile Impact (23° C.) D-1822S 1020 1020 865 1160760 1240 KJ/m² (ft.-lbs./in²) (485) (485) (410) (550) (360) (590) VicatTemperature, ° C. D-1525 63 62 58 73 61 73

[0089] Examples of the more pertinent acrylic acid based hard ionomerresin suitable for use in the present outer cover composition sold underthe “Iotek” trade name by the Exxon Corporation include Iotek 8000,8010, 8020, 8030, 7030, 7010, 7020, 1002, 1003, 959 and 960. Thephysical properties of lotek 959 and 960 are shown above. The typicalproperties of the remainder of these and other Iotek hard ionomerssuited for use in formulating the outer layer cover composition are setforth below in Table 9: TABLE 9 Typical Properties of Iotek IonomersASTM Method Units 4000 4010 8000 8020 8030 Resin Properties Cation typezinc zinc sodium sodium sodium Melt index D-1238 g/10 min. 2.5 1.5 0.81.6 2.8 Density D-1505 kg/m³ 963 963 954 960 960 Melting Point D-3417 °C. 90 90 90 87.5 87.5 Crystallization Point D-3417 ° C. 62 64 56 53 55Vicat Softening Point D-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid16 11 % of Acid Groups cation neutralized 30 40 Plaque Properties (3 mmthick, compression molded) Tensile at break D-638 MPa 24 26 36 31.5 28Yield point D-638 MPa none none 21 21 23 Elongation at break D-638 % 395420 350 410 395 1% Secant modulus D-638 MPa 160 160 300 350 390 ShoreHardness D D-2240 — 55 55 61 58 59 Film Properties (50 micron film 2.2:1Blow-up ratio) 4000 4010 8000 8020 8030 Tensile at Break MD D-882 MPa 4139 42 52 47.4 TD D-882 MPa 37 38 38 38 40.5 Yield point MD D-882 MPa 1517 17 23 21.6 TD D-882 MPa 14 15 15 21 20.7 Elongation at Break MD D-882% 310 270 260 295 305 TD D-882 % 360 340 280 340 345 1% Secant modulusMD D-882 MPa 210 215 390 380 380 TD D-882 MPa 200 225 380 350 345 DartDrop Impact D-1709 g/micron 12.4 12.5 20.3 ASTM Method Units 7010 70207030 Resin Properties Cation type zinc zinc zinc Melt Index D-1238 g/10min. 0.8 1.5 2.5 Density D-1505 kg/m³ 960 960 960 Melting Point D-3417 °C. 90 90 90 Crystallization Point D-3417 ° C. — — — Vicat SofteningPoint D-1525 ° C. 60 63 62.5 % Weight Acrylic Acid — — — % of AcidGroups Cation Neutralized — — — Plaque Properties (3 mm thick,compression molded) Tensile at break D-638 MPa 38 38 38 Yield PointD-638 MPa none none none Elongation at break D-638 % 500 420 395 1%Secant modulus D-638 MPa — — — Shore Hardness D D-2240 — 57 55 55

[0090] It has been determined that when hard/soft ionomer blends areused for the outer cover layer, good results are achieved when therelative combination is in a range of about 3-25 percent hard ionomerand about 75-97 percent soft ionomer.

[0091] Moreover, in alternative embodiments, the outer cover layerformulation may also comprise up to 100 wt % of a soft, low modulusnon-ionomeric thermoplastic material including a polyester polyurethanesuch as B.F. Goodrich Company's Estane® polyester polyurethane X-4517.The non-ionomeric thermoplastic material may be blended with a softionomer. For example, polyamides blend well with soft ionomer. Accordingto B.F. Goodrich, Estanes X-4517 has the following properties:Properties of Estane ® X-4517 Tensile 1430 100%  815 200% 1024 300% 1193Elongation  641 Youngs Modulus 1826 Hardness A/D 88/39 Bayshore Rebound 59 Solubility in Water Insoluble Melt processing temperature >350° F.(>177° C.) Specific Gravity (H₂O = 1) 1.1-1.3

[0092] Other soft, relatively low modulus non-ionomeric thermoplasticelastomers may also be utilized to produce the outer cover layer as longas the non-ionomeric thermoplastic elastomers produce the playabilityand durability characteristics desired without adversely effecting theenhanced travel distance characteristic produced by the high acidionomer resin composition. These include, but are not limited tothermoplastic polyurethanes such as Texin thermoplastic polyurethanesfrom Mobay Chemical Co. and the Pellethane thermoplastic polyurethanesfrom Dow Chemical Co.; non-ionomeric thermoset polyurethanes includingbut not limited to those disclosed in U.S. Pat. No. 5,334,673;cross-linked metallocene catalyzed polyolefins; ionomer/rubber blendssuch as those in Spalding U.S. Pat. No. 4,986,545; 5,098,105 and5,187,013; and, Hytrel polyester elastomers from DuPont and Pebaxpolyesteramides from Elf Atochem S. A. Dual Core

[0093] As noted, the present invention golf balls utilize a unique dualcore configuration. Preferably, the cores comprise (i) an interiorspherical center component formed from a thermoset material, athermoplastic material, or combinations thereof and (ii) a core layerdisposed about the spherical center component, the core layer formedfrom a thermoset material, a thermoplastic material, or combinationsthereof. Most preferably, the core layer is disposed immediatelyadjacent to, and in intimate contact with the center component. Thecores may further comprise (iii) an optional outer core layer disposedabout the core layer. Most preferably, the outer core layer is disposedimmediately adjacent to, and in intimate contact with the core layer.The outer core layer may be formed from a thermoset material, athermoplastic material, or combinations thereof.

[0094] The present invention provides several additionally preferredembodiment golf balls utilizing the unique dual core configuration andthe previously described cover layers. Referring to FIG. 3, a preferredembodiment golf ball 35 is illustrated comprising a core 30 formed froma thermoset material surrounded by a core layer 32 formed from athermoplastic material. A multi-layer cover 34 surrounds the core 30 andthe core layer 32. The multi- layer cover 34 preferably corresponds tothe previously described multi-layer cover 12.

[0095] As illustrated in FIG. 4, another preferred embodiment golf ball45 in accordance with the present invention is depicted. The preferredembodiment golf ball 45 comprises a core 40 formed from a thermoplasticmaterial surrounded by a core layer 42. The core layer 42 is formed froma thermoset material. A multi-layer cover 44 surrounds the core 40 andthe core layer 42. Again, the multi-layer cover 44 preferablycorresponds to the previously described multi-layer cover 12.

[0096]FIG. 5 illustrates yet another preferred embodiment golf ball 55in accordance with the present invention. The preferred embodiment golfball 55 comprises a core 50 formed from a thermoplastic material. A corelayer 52 surrounds the core 50. The core layer 52 is formed from athermoplastic material which may be the same as the material utilizedfor the core 50, or one or more other or different thermoplasticmaterials. The preferred embodiment golf ball 55 utilizes an optionalouter core layer 54 that surrounds the core component 50 and the corelayer 52. The outer core layer 54 is formed from a thermoplasticmaterial which may be the same or different than any of thethermoplastic materials utilized for the core 50 and the core layer 52.The golf ball 55 further comprises a multi-layer cover 56 that ispreferably similar to the previously described multi-layer cover 12.

[0097]FIG. 6 illustrates yet another preferred embodiment golf ball 65in accordance with the present invention. The preferred embodiment golfball 65 comprises a core 60 formed from a thermoplastic, thermosetmaterial, or any combination of a thermoset and thermoplastic material.A core layer 62 surrounds the core 60. The core layer 62 is formed froma thermoset material. The preferred embodiment golf ball 65 alsocomprises an optional outer core layer 64 formed from a thermoplasticmaterial. A multi-layer cover 66, preferably similar to the previouslydescribed multi-layer cover 12, is disposed about, and generallysurrounds, the core 60, the core layer 62 and the outer core 64.

[0098] A wide array of thermoset materials can be utilized in thepresent invention dual cores. Examples of suitable thermoset materialsinclude butadiene or any natural or synthetic elastomer, includingmetallocene polyolefins, polyurethanes, silicones, polyamides,polyureas, or virtually any irreversibly cross-linked resin system. Itis also contemplated that epoxy, phenolic, and an array of unsaturatedpolyester resins could be utilized.

[0099] The thermoplastic material utilized in the present invention golfballs and, particularly their dual cores, may be nearly anythermoplastic material. Examples of typical thermoplastic materials forincorporation in the golf balls of the present invention include, butare not limited to, ionomers, polyurethane thermoplastic elastomers, andcombinations thereof. It is also contemplated that a wide array of otherthermoplastic materials could be utilized, such as polysulfones,fluoropolymers, polyamide-imides, polyarylates, polyaryletherketones,polyaryl sulfones/polyether sulfones, polybenzimidazoles,polyether-imides, polyimides, liquid crystal polymers, polyphenylenesulfides; and specialty high-performance resins, which would includefluoropolymers, polybenzimidazole, and ultrahigh molecular weightpolyethylenes.

[0100] Additional examples of suitable thermoplastics includemetallocenes, polyvinyl chlorides, acrylonitrile-butadiene-styrenes,acrylics, styrene-acrylonitriles, styrene-maleic anhydrides, polyamides(nylons), polycarbonates, polybutylene terephthalates, polyethyleneterephthalates, polyphenylene ethers/polyphenylene oxides, reinforcedpolypropylenes, and high-impact polystyrenes.

[0101] Preferably, the thermoplastic materials have relatively highmelting points, such as a melting point of at least about 300° F.Several examples of these preferred thermoplastic materials and whichare commercially available include, but are not limited to, Capron (ablend of nylon and ionomer), Lexan polycarbonate, Pebax, and Hytrel. Thepolymers or resin system may be cross-linked by a variety of means suchas by peroxide agents, sulphur agents, radiation or other cross-linkingtechniques.

[0102] Any or all of the previously described components in the cores ofthe golf balls of the present invention may be formed in such a manner,or have suitable fillers added, so that their resulting density isdecreased or increased. For example, any of the components in the dualcores could be formed or otherwise produced to be light in weight. Forinstance, the components could be foamed, either separately or in-situ.Related to this, a foamed light weight filler agent may be added. Incontrast, any of these components could be mixed with, or otherwisereceive, various high density filler agents or other weightingcomponents such as relatively high density fibers or particulate agentsin order to increase their mass or weight.

[0103] The following commercially available thermoplastic resins areparticularly preferred for use in the noted dual cores employed in thegolf balls of the present invention: Capron 8351 (available from AlliedSignal Plastics), Lexan ML5776 (from General Electric), Pebax 3533 (apolyether block amide from Elf Atochem), and Hytrel G4074 (from DuPont).Properties of these four preferred thermoplastics are set forth below inTables 10-13. When forming a golf ball in accordance with the presentinvention, if the interior center component of the dual core is tocomprise a thermoplastic material, it is most preferred to utilize Pebaxthermoplastic resin. TABLE 10 CAPRON 8351 DAM 50% RH ASTM TestMECHANICAL Tensile Strength, Yield, 7,800 (54) — D-638 psi (MPa)Flexural Strength, psi 9,500 (65) — D-790 (MPa) Flexural Modulus,230,000 (1,585) — D-790 psi (MPa) Ultimate Elongation, % 200 — D-638Notched Izod Impact, No Break — D-256 ft-lbs/in (J/M) Drop WeightImpact, 150 (200) — D-3029 ft-lbs (J) Drop Weight Impact, 150 (200) —D-3029 @ −40° F., ft-lbs (J) PHYSICAL Specific Gravity 1.07 — D-792THERMAL Melting Point, ° F. (° C.) 420 (215) — D-789 Heat Deflection @140 (60) — D-648 264 psi ° F. (° C.)

[0104] TABLE 11 Lexan ML5776 TYPICAL PROPERTY DATA UNIT METHODMECHANICAL Tensile Strength, yield, 8500 psi ASTM D 638 Type I, 0.125″Tensile Strength, break, 9500 psi ASTM D 638 Type I, 0.125″ TensileElongation, yield, 110.0 % ASTM D 638 Type I, 0.125″ Flexural Strength,yield, 12000 psi ASTM D 790 0.125″ Flexural Modulus, 310000 psi ASTM D790 0.125″ IMPACT Izod Impact, unnotched, 60.0 ft-lb/in ASTM D 4812 73°F. Izod Impact, notched, 15.5 ft-lb/in ASTM M 256 73° F. Izod Impact,notches, 12.0 ft-lb/in ASTM D 256 73° F., 0.250″ Instrumented Impact48.0 ft-lbs ASTM D 3763 Energy @ Peak, 73° F. THERMAL HDT, 264 psi,0.250″, 257 deg F. ASTM D 648 unannealed Thermal Index, 80 deg C. UL7468 Elec Prop Thermal Index, 80 deg C. UL 7468 Mech Prop with impactThermal Index, 80 deg C. UL 7468 Mech Prop without impact PHYSICALSpecific Gravity, solid 1.19 — ASTM D 792 Water Absorption, 0.150 % ASTMD 570 24 hours @ 73° F. Mold Shrinkage, 5.7 in/in E-3 ASTM D 955 flow,0.125″ Melt Flow Rate, nom'l, 7.5 p/10 min ASTM D 1238 300° C./1.2 kgf(0) FLAME CHARACTERISTICS UL File Number, USA E121562 — — 94HB Rated(tested thickness) 0.060 inch UL 94

[0105] TABLE 12 PEBAX ® 3533 RESIN ASTM TEST PROPERTY METHOD UNITS 3533Specific Gravity D792 Water Absorption 0.5 Equilibrium (20° C., 50%RH.>) 24 Hr. Immersion D570 1.2 Hardness D2240 35D Tensile Strength,D638 psi 5600 Ultimate Elongation, Ultimate D638 % 580 Flexural ModulusD790 psi 2800 Izod Impact, Notched D256 ft-   20° C. lb./in. NB −40° C.NB Abrasion Resistance D1044 Mg/1000 104 H18/1000 g Cycles TearResistance Notched D624C lb./in. 260 Melting Point D3418 ° F. 306 VicatSoftening Point D1525 ° F. 165 HDT 66 psi D648 ° F. 115 Compression SetD395A % 54 (24 hr., 160° F.)

[0106] TABLE 13 HYTREL G4074 Thermoplastic Elastomer PHYSICAL Dens/Sp GrASTM D792 1.1800 sp gr 23/23C Melt Flow ASTM D1238 5.20 @ E-190° C./2.16kg g/10/min Wat Abs ASTM D570 2.100% MECHANICAL Elong @ Brk ASTM D638230.0% Flex Mod ASTM D790 9500 psi TnStr @ Brk ASTM D638 2000 psi IMPACTNotch Izod ASTM D256 No Break @ 73.0° F. @ 0.2500 inft-lb/in 0.50 @−40.0° F. @ 0.2500 inft-lb/in HARDNESS Shore ASTM D2240 40 Shore DTHERMAL DTUL @ 66 ASTM D648 122° F. Melt Point 338.0° F. Vicat Soft ASTMD1525 248° F. Melt Point

[0107] The cores of the inventive golf balls typically have acoefficient of restitution of about 0.750 or more, more preferably 0.770or more and a PGA compression of about 90 or less, and more preferably70 or less. The cores have a weight of 25-40 grams and preferably 30-40grams. The core can be compression molded from a slug of uncured orlightly cured elastomer composition comprising a high cis contentpolybutadiene and a metal salt of an α, β, ethylenically unsaturatedcarboxylic acid such as zinc mono- or diacrylate or methacrylate. Toachieve higher coefficients of restitution and/or to increase hardnessin the core, the manufacturer may include a small amount of a metaloxide such as zinc oxide. In addition, larger amounts of metal oxidethan are needed to achieve the desired coefficient may be included inorder to increase the core weight so that the finished ball more closelyapproaches the U.S.G.A. upper weight limit of 1.620 ounces. Non-limitingexamples of other materials which may be used in the core compositionincluding compatible rubbers or ionomers, and low molecular weight fattyacids such as stearic acid. Free radical initiator catalysts such asperoxides are admixed with the core composition so that on theapplication of heat and pressure, a curing or cross-linking reactiontakes place.

[0108] Wound cores are generally produced by winding a very long elasticthread around a solid or liquid filled balloon center. The elasticthread is wound around the center to produce a finished core of about1.4 to 1.6 inches in diameter, generally. However, the preferredembodiment golf balls of the present invention preferably utilize asolid core, or rather a solid dual core configuration, as opposed to awound core.

[0109] Method of Making Golf Balls

[0110] In preparing preferred embodiment golf balls in accordance withthe present invention, a hard inner cover layer is molded (by injectionmolding or by compression molding) about a core (preferably a solidcore, and most preferably a dual core). A comparatively softer outerlayer is molded over the inner cover layer.

[0111] The dual cores of the present invention are preferably formed bycompression molding techniques. However, it is fully contemplated thatliquid injection molding or transfer molding techniques could beutilized.

[0112] For purposes of example, a preferred method of making the golfball 45 depicted in FIG. 4 is as follows. Specifically, a thermosetmaterial, i.e. a core layer 42, is formed about an inner core component40 comprising a thermoplastic material as follows. Referring to FIG. 7,preforms 75 of a thermoset material, i.e. utilized to form the corelayer 42, are preheated in an oven for one-half hour at 170° F. andplaced in the bottom 73 of a molding assembly 70. A Teflon-coated plate76 with two hemispheres 77 and 78, each about 0.840 inches in diameter,is placed on top of the preforms. Additional preforms, preheated asdescribed above, are placed in the corresponding cavities of a top mold72. The bottom mold 73 is engaged with the top mold 72 and the assemblyflipped or otherwise inverted. The bottom one half of the mold assembly70 then becomes the top one half of the mold assembly. The mold assembly70 is then placed in a press and cold formed at room temperature usingapproximately 10 tons of pressure in a steam press. The molding assembly70 is closed for approximately two minutes and pressure released. Themolding assembly 70 is then opened and the Teflon plate 76 is removedthereby leaving one or more essentially perfectly formed one-half shellsor cavities in the thermoset material. Previously formed thermoplasticcore centers are then placed in the bottom cavities and the top portion72 of the molding assembly 70 is placed on the bottom 73 and thematerials disposed therebetween cured. The golf ball produced by thismethod had an inner core diameter of 0.840 inches in diameter. The outercore diameter had a final diameter of 1.470 inches, and a pre-molddiameter of 1.490 inches. A relatively hard inner cover layer is thenmolded about the resulting dual core component. The diameter of theinner cover was 1.570 inches. A comparatively softer outer cover layeris then molded about the inner cover layer. The outer cover diameter was1.680 inches. Details of molding the inner and outer covers are setforth below.

[0113] Four golf balls in accordance with the present invention wereformed, each using a preferred and commercially available high meltingpoint thermoplastic material as an inner core component. Table 14, setforth below, summarizes these balls. TABLE 14 Lexan Control Capron MLPebax Hytrel (Single 8351 5776-7539 3533 G-4074 Core) Inner Core size(inches) 0.835 0.854 0.840 0.831 — weight (grams) 5.33 6.14 5.08 5.81 —rebound % (100″) 78 83 65 61 — Shore C (surface) — — 57 73 — Shore D(surface) 75 83 36 47 — Outer Core Formulation Cis 1,4 Polybutadiene 100100 100 100 100 Zinc oxide 27 26 28 21 25 Zinc stearate 16 16 16 16 15Zinc diacrylate 20 20 24 24 18 231 × L 0.9 0.9 0.9 0.9 0.9 163.9 162.9168.9 161.9 158.9 Double Core Properties size (inches) 1.561 1.560 1.5621.563 1.562 weight (grams) 37.7 37.8 37.8 37.5 37.8 compression (riehle)79 80 99 93 114 COR .689 .603 .756 .729 .761 Molded Ball Properties size(inches 1.685 1.683 1.682 1.683 1.685 weight (grams) 45.3 45.5 45.5 45.245.4 compression (riehle) 78 80 89 87 102 COR .750 .667 .785 .761 .788Cover Stock (used on all above balls) surlyn 8940 22 *T.G. MB Iotek 703075.35 surlyn 9910 54.5 Unitane 0-110 23.9 surlyn 8320 10 Ultra MarineBlue 0.46 surlyn 8120 4 Eastonbrite OB-1 0.26 T.B. MB* 9.5 Santonox R0.038 100.0 100.00

[0114] Generally, the inner cover layer which is molded over the core,or preferably a dual core component, is about 0.01 inches to about 0.10inches in thickness, preferably about 0.03-0.07 inches thick. The innerball which includes the core and inner cover layer preferably has adiameter in the range of 1.25 to 1.60 inches. The outer cover layer isabout 0.01 inches to about 0.10 inches in thickness. Together, the core,the inner cover layer and the outer cover layer combine to form a ballhaving a diameter of 1.680 inches or more, the minimum diameterpermitted by the rules of the United States Golf Association andweighing no more than 1.62 ounces.

[0115] Most preferably, the resulting golf balls in accordance with thepresent invention have the following dimensions: Size Specifications:Preferred Most Preferred Inner Core Max. 1.250″ 1.00″ Min. 0.500″ 0.70″Outer Core Max. 1.600″ 1.570″ Min. 1.500″ 1.550″ Cover Thickness (Total)Max. 0.090″ 0.065″ Min. 0.040″ 0.055″

[0116] In a particularly preferred embodiment of the invention, the golfball has a dimple pattern which provides coverage of 65% or more. Thegolf ball typically is coated with a durable, abrasion-resistant,relatively non-yellowing finish coat.

[0117] The various cover composition layers of the present invention maybe produced according to conventional melt blending procedures.Generally, the copolymer resins are blended in a Banbury type mixer,two-roll mill, or extruder prior to neutralization. After blending,neutralization then occurs in the melt or molten states in the Banburymixer. Mixing problems are minimal because preferably more than 75 wt %,and more preferably at least 80 wt % of the ionic copolymers in themixture contain acrylate esters and, in this respect, most of thepolymer chains in the mixture are similar to each other. The blendedcomposition is then formed into slabs, pellets, etc., and maintained insuch a state until molding is desired. Alternatively, a simple dry blendof the pelletized or granulated resins which have previously beenneutralized to a desired extent and colored masterbatch may be preparedand fed directly into the injection molding machine where homogenizationoccurs in the mixing section of the barrel prior to injection into themold. If necessary, further additives such as an inorganic filler, etc.,may be added and uniformly mixed before initiation of the moldingprocess. A similar process is utilized to formulate the high acidionomer resin compositions used to produce the inner cover layer. In oneembodiment of the invention, a masterbatch of non-acrylateester-containing ionomer with pigments and other additives incorporatedtherein is mixed with the acrylate ester-containing copolymers in aratio of about 1-7 weight W masterbatch and 93-99 weight % acrylateester-containing copolymer.

[0118] The golf balls of the present invention can be produced bymolding processes which include but are not limited to those which arecurrently well known in the golf ball art. For example, the golf ballscan be produced by injection molding or compression molding the novelcover compositions around a wound or solid molded core to produce aninner ball which typically has a diameter of about 1.50 to 1.67 inches.The core, preferably of a dual core configuration, may be formed aspreviously described. The outer layer is subsequently molded over theinner layer to produce a golf ball having a diameter of 1.620 inches ormore, preferably about 1.680 inches or more. Although either solid coresor wound cores can be used in the present invention, as a result oftheir lower cost and superior performance solid molded cores arepreferred over wound cores. The standards for both the minimum diameterand maximum weight of the balls are established by the United StatesGolf Association (U.S.G.A.).

[0119] In compression molding, the inner cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in a moldhaving the desired inner cover thickness and subjected to compressionmolding at 200° to 300° F. for about 2 to 10 minutes, followed bycooling at 50° to 70° F. for about 2 to 7 minutes to fuse the shellstogether to form a unitary intermediate ball. In addition, theintermediate balls may be produced by injection molding wherein theinner cover layer is injected directly around the core placed at thecenter of an intermediate ball mold for a period of time in a moldtemperature of from 50° to about 100° F. Subsequently, the outer coverlayer is molded around the core and the inner layer by similarcompression or injection molding techniques to form a dimpled golf ballof a diameter of 1.680 inches or more.

[0120] After molding, the golf balls produced may undergo variousfurther processing steps such as buffing, painting and marking asdisclosed in U.S. Pat. No. 4,911,451.

[0121] The resulting golf ball produced from the hard inner layer andthe relatively softer, low flexural modulus outer layer provide for animproved multi-layer golf ball having a unique dual core configurationwhich provides for desirable coefficient of restitution and durabilityproperties while at the same time offering the feel and spincharacteristics associated with soft balata and balata-like covers ofthe prior art.

[0122] The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon a reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

What is claimed:
 1. A golf ball comprising: a dual core having a centercomponent and a core layer disposed about said center component; and, acover layer disposed about said dual core; wherein said center componentcomprises a thermoset material and said core layer comprises athermoplastic material; wherein said cover layer includes at least asingle outer cover layer having a Shore D hardness of from about 40 to60.
 2. The golf ball of claim 1 wherein said thermoset materialcomprises a material selected from the group consisting of (i) adiene-containing polymer, (ii) a metallocene catalyzed polyolefin thatis crosslinked, (iii) a polyurethane, (iv) a silicone, (v) a polyamide,(vi) a polyurea, and (vii) combinations thereof; and said thermoplasticmaterial comprises a material selected from the group consisting of (i)an ionomer, (ii) a polyurethane, (iii) an elastomer, (iv) apolyetheramide, (v) a polyetherester, (vi) a metallocene catalyzedpolyolefin, (vii) a styrene butadiene block copolymer, and (viii)combinations thereof.
 3. The golf ball of claim 1 wherein said corelayer comprises more than one layer.
 4. The golf ball of claim 1 whereinsaid thermoset material comprises a polybutadiene rubber.
 5. The golfball of claim 1 wherein said thermoset material comprises apolyurethane.
 6. The golf ball of claim 1 wherein said thermoplasticmaterial comprises a material selected from the group consisting of (i)polyurethane, (ii) polyester, (iii) polyamide, (iv) ionomer, (v)polycarbonate, (vi) polyether block amide, and (vii) combinationsthereof.
 7. The golf ball of claim 1 wherein said center component ofsaid dual core has an outer diameter of from about 0.500 inches to about1.250 inches, and said dual core has an outer diameter of from about1.25 to about 1.600 inches.
 8. The golf ball of claim 1 wherein at leastone of said core layer and said center component of said dual corecomprise a density increasing agent.
 9. The golf ball of claim 1 whereinat least one of said core layer and said center component of said dualcore comprise an agent that is foamed or otherwise reduced in density.10. A multi-layer golf ball comprising: a dual core having a centercomponent and a core layer disposed about said center component; and atleast one cover layer disposed about said dual core; wherein said centercomponent comprises a thermoset material and said core layer comprises athermoplastic material; wherein said cover layer includes at least asingle outer cover layer having a Shore D hardness of from about 40 to50.
 11. The golf ball of claim 10 wherein said thermoset materialcomprises a material selected from the group consisting of (i) adiene-containing polymer, (ii) a metallocene catalyzed polyolefin thatis crosslinked, (iii) a polyurethane, (iv) a silicone, (v) a polyamide,(vi) a polyurea, and (vii) combinations thereof; and said thermoplasticmaterial comprises a material selected from the group consisting of (i)an ionomer, (ii) a polyurethane, (iii) an elastomer, (iv) apolyetheramide, (v) a polyetherester, (vi) a metallocene catalyzedpolyolefin, (vii) a styrene butadiene block copolymer, and (viii)combinations thereof.
 12. The golf ball of claim 10 wherein said corelayer comprises more than one layer.
 13. The golf ball of claim 10wherein said thermoset material comprises a polybutadiene rubber. 14.The golf ball of claim 10 wherein said thermoset material comprises apolyurethane.
 15. The golf ball of claim 10 wherein said thermoplasticmaterial comprises a material selected from the group consisting of (i)polyurethane, (ii) polyester, (iii) polyamide, (iv) ionomer, (v)polycarbonate, (vi) polyether block amide, and (vii) combinationsthereof.
 16. The golf ball of claim 10 wherein said center component ofsaid dual core has an outer diameter of from about 0.500 inches to about1.250 inches, and said dual core has an outer diameter of from about1.25 to about 1.600 inches.
 17. The golf ball of claim 10 wherein atleast one of said core layer and said center component of said dual corecomprise a density increasing agent.
 18. The golf ball of claim 10wherein at least one of said core layer and said center component ofsaid dual core comprise an agent that is foamed or otherwise reduced indensity.